The present invention relates generally to injection molding and die casting systems. In particular, the present invention relates to vacuum blocks and vent blocks used with injection molding and die casting systems.
Injection molding and die casting processes typically incorporate stationary and movable mold halves, which open and close along a parting line to define a cavity where the molding or casting manufacturing material is injected. Stationary mold halves, also known as fixed-die halves, fixed holder blocks, or cover blocks, are mounted to stationary platens. In contrast, movable mold halves, also known as movable-die halves, movable holder blocks, or ejector halves, are capable of moving relative to the stationary mold half for opening and closing the cavity. Movable mold halves are mounted to ejector platens, which are generally connected to hydraulic actuators for providing the movement required for ejecting the manufactured part.
Vacuum assistance in injection molding and die casting processes has been utilized to varying degrees for optimizing product quality. The general intent of the vacuum is to improve the production of injection molding and die casting by removing gases from within the molding and casting cavities. These improvements include higher surface quality, reduced level of porosity, and greater mechanical characteristics such as strength. Vacuum assistance generally requires the use of a vacuum pump, a vacuum line connecting the pump to the molding or casting cavity, and a means for preventing injected material from overflowing into the vacuum system. One approach for preventing the flow of the injected material is with an automated or manual valve located along the vacuum line. The purpose of the valve is to stop the flows of the vacuum and the injected material before the material enters the vacuum system.
An alternative approach for preventing overflow of the injected material is with gas purging blocks, such as a vacuum block or a vent block. Vacuum blocks typically comprise block-halves that are connected to the stationary and movable mold halves. The vacuum block simultaneously provides a gas purge passage for allowing the vacuum to remove the gases, and allows the excess injected material to solidify during the drawing of the vacuum. The solidified material functions as a stopper, preventing further manufacturing material from flowing out of the vacuum block and into the vacuum system. As such, vacuum blocks preclude the need for mechanical valves.
Similarly, vent blocks allow gases to be purged from the cavity of a molding or casting system by the force of the injected material flowing into the cavity. If the injected material is not stopped, it will continue to overflow out of the vent block with the purged gas. The vent block allows the injected material to solidify within the gas purge passage during the injection process, effectively stopping-up the gas path to permit the injected material to fully fill the cavity. As with vacuum blocks, the solidified material must be ejected from the vent block along with the new product being ejected from the mold or die cavity. Typically, with both vacuum blocks and vent blocks, the overflow material that solidifies in the blocks is cut from the molded products and recycled back into the raw materials for further use after ejection.
Vacuum and vent blocks typically utilize mating corrugated faces to form a gas purge passage having a uniform cross-sectional area. Uniform gas purge passages extend generally straight across the block-halves in a transverse direction, and extend longitudinally across the block-halves over a uniform corrugation pattern. The corrugated faces provide a high surface area aver which heat is drawn away from the overflowing material. However, the circuitous path formed by the corrugated faces also increases the surface area over which the solidified material bonds to the block halves, thereby making parting of the mold halves difficult. There is, therefore, a continuing need to improve the heat transfer properties of corrugated faces in vacuum and vent blocks, while also permitting the solidified material to be easily removed.